Psychologists have long understood that observing people in a laboratory can give them only a rough imitation of what happens in real life. Yet, how can the influence of the "real" world, with all its complexity and variability, best be measured? This book offers intriguing new ways of measuring the influence of environmental factors on individual human behavior. Opening with a provocative theoretical essay by Urie Bronfenbrenner, the book offers both theoretical models and testing methods for quantifying the natural environment at each stage of development.